Method for making transition metal dichalcogenide crystal

ABSTRACT

A method for making a transition metal dichalcogenide crystal having a chemical formula represented as MX2 is provided, wherein M represents a central transition metal element, and X represents a chalcogen element. The method includes providing a MX2 polycrystalline powder, a MX2 seed crystal, and a transport medium. The MX2 polycrystalline powder and the transport medium are placed in a first reaction chamber. The first reaction chamber and the MX2 seed crystal are placed in a second reaction chamber having a source end and a deposition end opposite to the source end. The first reaction chamber is placed at the source end, and the MX2 seed crystal is placed at the deposition end.

FIELD

The present application relates to a technical field of materials, inparticular to a transition metal dichalcogenide crystal.

BACKGROUND

Transition metal dichalcogenides (TMDs) have attracted widespreadattention due to their unique electrical and optical properties. Thechemical formula of the transition metal dichalcogenides can berepresented as MX₂, wherein M represents a central transition metalelement (for example, IV, V, VI, VII, IX or X group element), and Xrepresents a chalcogen element (for example, S, Se or Te).

Currently methods for making bulk transition metal dichalcogenides areby chemical vapor transport (CVT) method. However, existing CVT methodsusually nucleates at multiple locations on the inner wall of thereaction chamber, which may limit the final size of the crystals andgenerate aggregated small crystal clusters. Thus, it is may be difficultto prepare large-sized and high-quality transition metaldichalcogenides.

Therefore, there is room for improvement in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof embodiments, with reference to the attached figures, wherein:

FIG. 1 shows a schematic process flow of a method for making atransition metal dichalcogenide crystal of an embodiment according topresent disclosure.

FIG. 2 shows a schematic view of a CVT device for growing a seedaccording to an embodiment of the present disclosure.

FIG. 3 shows a CVT growth temperature gradient curve of an embodiment ofthe present disclosure.

FIG. 4 shows a schematic view of a conventional CVT device for growingMX2 crystal.

FIG. 5A shows a photo of a MoSe₂ crystal prepared by the method of FIG.1 .

FIG. 5B shows a photo of a MoTe₂ crystal prepared by the method of FIG.1 .

FIG. 5C shows a photo of a PtSe₂ crystal prepared by the method of FIG.1 .

FIG. 6A shows a photo of a MoSe₂ crystal prepared by the conventionalCVT growth method shown in FIG. 4 .

FIG. 6B shows a photo of a MoTe₂ crystal prepared by the conventionalCVT growth method shown in FIG. 4 .

FIG. 6C shows a photo of a PtSe₂ crystal prepared by the conventionalCVT growth method shown in FIG. 4 .

FIG. 7 shows powder X-ray diffraction (PXRD) patterns of MoSe₂ crystalsprepared by the method of FIG. 1 of the present disclosure and by theconventional CVT growth method shown in FIG. 4 .

FIG. 8 shows powder X-ray diffraction (PXRD) patterns of MoTe₂ crystalsprepared by the method of FIG. 1 of the present disclosure and by theconventional CVT growth method shown in FIG. 4 .

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. The drawings are not necessarily to scale, andthe proportions of certain parts may be exaggerated to illustratedetails and features better. The description is not to be considered aslimiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now bepresented.

The term “substantially” is defined to be essentially conforming to theparticular dimension, shape or other word that substantially modifies,such that the component need not be exact. For example, substantiallycylindrical means that the object resembles a cylinder, but can have oneor more deviations from a true cylinder. The term “comprising” means“including, but not necessarily limited to”; it specifically indicatesopen-ended inclusion or membership in a so-described combination, group,series and the like.

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

An infrared absorber of a first embodiment is a carbon nanotubestructure formed by stacking a plurality of drawn carbon nanotube films.

Referring to FIG. 1 and FIG. 2 , a method for making a transition metaldichalcogenide crystal of one embodiment is provided. The chemicalformula of the transition metal dichalcogenide crystal can berepresented as MX₂, wherein M represents a central transition metalelement (for example, IV, V, VI, VII, IX or X group element), and Xrepresents a chalcogen element (for example, S, Se or Te). In oneembodiment, the MX₂ can be MoS₂, MoSe₂, MoTe₂, PtSe₂, PtS₂, PtTe₂, WSe₂,WTe₂, ReSe₂, ReS₂, VS₂, VSe₂, CrSe, CrSe₂, PdS₂, PdSe₂, PdTe₂, TiS₂,TiSe₂, NbS₂, NbSe₂, TaS₂, TaSe₂, and so on.

The method for making the transition metal dichalcogenide crystalincludes one or more of the following steps:

S10, providing MX₂ polycrystalline powder 11 and MX₂ seed crystal 13;

S20, providing a first reaction chamber 31 with an opening 311 at oneend of the first reaction chamber 31, wherein the MX₂ polycrystallinepowder 11 and a transport medium 15 are placed in the first reactionchamber 31; and

S30, providing a second reaction chamber 33, wherein the second reactionchamber 33 is a vacuum-sealed chamber, the second reaction chamber 33has a source end and a deposition end opposite to the source end, thefirst reaction chamber 31 and the MX₂ seed crystal 13 are placed in thesecond reaction chamber 33 for CVT growth, the first reaction chamber 31is placed at the source end, and the MX₂ seed crystal 13 is placed atthe deposition end.

During step S10, the MX₂ polycrystalline powder 11 is aone-hundred-micrometer-level and non-obviously shiny powder. The MX₂polycrystalline powder 11 is prone to have twin crystals, grainboundaries or rough surfaces.

The MX₂ polycrystalline powder 11 can be obtained by direct solid-statereaction of a mixture of high purity M element and high purity Xelement. The high purity refers to a purity range of 99% to 99.99999%.For example, in one embodiment, the purity of Mo is 99.95%, the purityof Pt is 99.9%, the purity of Se is 99.999%, and the purity of Te is99.999%. The above-mentioned mixture of M element and X element isgradually heated to the reaction temperature at a certain rate undervacuum conditions and remained for a period of time to obtain the MX₂polycrystalline powder 11 as a precursor. The certain rate can be lessthan 20 Kelvin/min. In one embodiment, the mixture of M element and Xelement is heated to 1073 Kelvin at a rate of 5 Kelvin/min in a vacuumquartz ampoule, and is remained at 1073 Kelvin for 3 days.

The MX₂ seed crystal 13 is a single crystal with a size ranging from 500μm (micrometer) to 1 mm (millimeter). The MX₂ seed crystal 13 has aregular shape and usually has a glossy appearance without obvious grainboundaries, twin crystals, or rough surfaces.

The MX₂ seed crystal 13 can be prepared by using the above-mentioned MX₂polycrystalline powder 11. For example, in one embodiment, the MX₂ seedcrystal 13 is prepared by the chemical vapor transport (CVT) method. Themethod for making the MX₂ seed crystal 13 includes the following steps:

S101, placing the MX₂ polycrystalline powder 11 and the transport medium15 in a chamber for CVT growing, to obtain MX₂ crystal;

S102, removing the remaining transport medium 15 in the MX₂ crystal; and

S103, selecting the MX₂ crystal with a size range of 500 microns to 1 mmas the MX₂ seed crystal 13.

During step S101, the chamber is a vacuum-sealed reaction chamber, thematerial of the chamber can be quartz, and the chamber can be a quartztube. The chamber is arranged horizontally within a temperaturegradient, and the temperature gradient can be generated by a tubefurnace that is also placed horizontally. Referring to FIG. 3 , FIG. 3shows a temperature gradient in the tube furnace, wherein T_(H)represents the temperature in the high temperature zone (source end),T_(D) represents the temperature in the low temperature zone (depositionend), and the temperature in the tube furnace gradually decreases fromthe source end to the deposition end. ΔT_(HD) represents the temperaturedifference between the source end and the deposition end. In oneexample, ΔT_(HD) is about 50K.

The transport medium 15 can be selected according to the MX₂polycrystalline powder 11, for example, when the MX₂ polycrystallinepowder 11 is MoSe₂, the transport medium 15 can be SeCl₄; when the MX₂polycrystalline powder 11 is MoTe₂, the transport medium 15 is TeBr₄;and when the MX₂ polycrystalline powder 11 is PtSe₂, the transportmedium 15 can be SeCl₄.

During step S102, the MX₂ crystal obtained in the step S10 l can bewashed with deionized water, acetone or ethanol to remove the remainingtransport medium 15.

During step S103, the size of the MX₂ crystal selected as the MX₂ seedcrystal 13 has certain requirements, and the size of the MX₂ crystal isin a range from 500 μm (micron) to 1 mm. In one embodiment, the MX₂crystal should have a gloss on the surface. If it does not have asurface gloss, it indicates that the seed crystal is of poor quality,has many defects, and the surface is not smooth enough, which is notconducive to the subsequent growth of large-sized crystals. In oneembodiment, the MX₂ crystal can be cut to a certain degree to form aregular shape, such as a regular hexagon, a regular triangle, a square,and the like.

During step S20, the material of the first reaction chamber 31 can bequartz, and one end of the first reaction chamber 31 has the opening311. The length of the first reaction chamber 31 can be in a range fromabout 2 cm (centimeter) to about 6 cm. The distance between the MX₂polycrystalline powder 11 and the opening 311 can be in a range fromabout 2 cm to about 6 cm. The minimum inner diameter of the firstreaction chamber 31 is greater than 1 mm. In one embodiment, the firstreaction chamber 31 is a quartz tube with a length of about 4 cm, anouter diameter of about 5 mm, and an inner diameter of about 3 mm.

The transport medium 15 of the step 20 is the same as the transportmedium 15 of the step 101, and the transport medium 15 can be selectedaccording to the MX₂ polycrystalline powder 11. For example, when theMX₂ polycrystalline powder 11 is MoSe₂, the transport medium 15 can beSeCl₄; when the MX₂ polycrystalline powder 11 is MoTe₂, the transportmedium 15 can be TeBr₄; and when the MX₂ polycrystalline powder 11 isPtSe₂, the transport medium 15 can be SeCl₄.

The MX₂ polycrystalline powder 11 and the transport medium 15 are bothplaced inside the first reaction chamber 31. In one embodiment, thefirst reaction chamber 31 is placed horizontally, and the MX₂polycrystalline powder 11 and the transport medium 15 are arranged awayfrom the opening 311 of the first reaction chamber 31. The distancebetween the MX₂ polycrystalline powder 11 and the opening 311 rangesfrom about 2 cm to about 6 cm. The distance between the transport mediumand the opening 311 ranges from about 2 cm to about 6 cm.

During step S30, the material of the second reaction chamber 33 can bequartz. Compared with the first reaction chamber 31, the second reactionchamber 33 has a larger volume to ensure that the first reaction chamber31 can be inserted into the second reaction chamber 33. The length ofthe second reaction chamber 33 can be in a range from about 7 cm toabout 11 cm. In one embodiment, the second reaction chamber 33 is aquartz tube with a length of about 9 cm, an outer diameter of about 9mm, and an inner diameter of about 7 mm.

During CVT growth, the first reaction chamber 31 is placed at the sourceend, and the MX₂ seed crystal 13 is placed at the deposition end. In oneembodiment, the opening 311 of the first reaction chamber 31 faces andcloses to the end point of the second reaction chamber 33, and is awayfrom the MX₂ seed crystal 13.

The second reaction chamber 33 is horizontally arranged within atemperature gradient, and the temperature gradient can be generated by atube furnace that is also placed horizontally. Referring to FIG. 3 forthe temperature gradient in the tube furnace. In FIG. 3 , T_(H)represents the temperature at the opening 311 of the first reactionchamber 31, T_(S) represents the temperature at the position of the MX₂polycrystalline powder 11 and the transport medium 15 in the firstreaction chamber 31, and T_(D) represents the temperature at thedeposition end of the second reaction chamber 33, ΔT_(HD) represents thedifference between the temperature at the opening 311 and thetemperature at the deposition end, and ΔT_(SH) represents thetemperature difference between the two opposite ends of the firstreaction chamber 31. In one embodiment, ΔT_(HD) is in a range from 45Kto 55K, and ΔT_(SH) is in a range from −15K to −5K. In one embodiment,ΔT_(HD) is about 50K, and ΔT_(SH) is about −10K.

Table 1 shows three groups of parameters and time required for thegrowth of MX₂ crystals (MoSe₂, MoTe₂, PtSe₂) using the method providedin this embodiment.

TABLE 1 the parameters and time of growing MX₂ crystal using the methodprovided in this implementation example example 1 example 2 example 3MX₂ crystal MoSe₂ crystal MoTe₂ crystal PtSe₂ crystal MX₂ powder (mg ·cm⁻³) MoSe₂ (≤11.0) MoTe₂ (≤6.6) PtSe₂ (≤22.1) transport medium (mg ·cm⁻³) SeCl₄ (≤2.21) TeBr₄ (≤3.32) SeCl₄ (≤11.0) T_(H) (K) 1223 1123 1273T_(D) (K) 1173 1073 1223 growth time (h) 24 24 72

The following provides three groups of experimental data using theexisting CVT method to prepare MX₂ crystals as comparative data toverify that the method for making the transition metal dichalcogenidecrystal of the present invention has better effect than the conventionaland existing CVT method.

FIG. 4 shows a schematic view of a conventional and existing CVT devicefor growing MX₂ crystal. The conventional and existing CVT method forgrowing MX₂ crystal used in the comparative example includes followingsteps:

placing the MX₂ polycrystalline powder 11 and the transport medium 15 ina third reaction chamber 35 for CVT growth, to obtain MX2 crystals.

The third reaction chamber 35 is a vacuum-sealed chamber, and the MX₂polycrystalline powder 11 and the transport medium 15 are placed at thesource end of the third reaction chamber 35. The third reaction chamber35 is horizontally arranged in a temperature gradient, and thetemperature gradient can be generated by a tube furnace that is alsoplaced horizontally. Referring to FIG. 3 for the temperature gradient inthe tube furnace. In FIG. 3 , T_(H) represents the temperature in thehigh temperature zone (source end), T_(D) represents the temperature inthe low temperature zone (deposition end), the temperature in the tubefurnace gradually decreases from the source end to the deposition end,and ΔT_(HD) represents the difference between the temperature at thesource end and the deposition end. In the comparative example, ΔT_(HD)is about 50K.

Table 2 shows the three groups of parameters and time required for thegrowth of MX₂ crystals using the conventional and existing CVT method.

TABLE 2 the parameters and time of using the conventional and existingCVT method to grow MX₂ crystal comparison example comparison comparisoncomparison example 1 example 2 example 3 MX₂ crystals MoSe₂ crystalsMoTe₂ crystals PtSe₂ crystals MX₂ powder (mg · cm⁻³) MoSe₂ (≤11.0) MoTe₂(≤6.6) PtSe₂ (≤22.1) transport medium (mg · cm⁻³) SeCl₄ (≤2.21) TeBr₄(≤3.32) SeCl₄ (≤11.0) T_(H) (K) 1223 1123 1273 T_(D) (K) 1173 1073 1223growth time (h) 72 72 504

By comparing Table 1 and Table 2, it can be found that the method formaking the transition metal dichalcogenide crystal of the presentapplication can significantly shorten the time required for the growthof MX₂ crystals. The growth time of MoSe₂, MoTe₂, and PtSe₂ crystals isrespectively changed from 72 hours, 72 hours, and 504 hours areshortened to 24 hours, 24 hours, and 72 hours.

FIG. 5A shows a photo of a MoSe₂ crystal prepared by the method formaking the transition metal dichalcogenide crystal of the presentapplication. FIG. 5B shows a photo of a MoTe₂ crystal prepared by themethod for making the transition metal dichalcogenide crystal of thepresent application. FIG. 5C shows a photo of a PtSe₂ crystal preparedby the method for making the transition metal dichalcogenide crystal ofthe present application. FIG. 6A shows a photo of a MoSe₂ crystalprepared by the conventional CVT growth method of the comparisonexample 1. FIG. 6B shows a photo of a MoTe₂ crystal prepared by theconventional CVT growth method of the comparison example 2. FIG. 6Cshows a photo of a PtSe₂ crystal prepared by the conventional CVT growthmethod of the comparison example 3. It can be seen from FIGS. 5A-5C andFIGS. 6A-6C that the products prepared by the comparative method(conventional CVT method) are generally aggregated small crystalclusters, and the size is usually limited between 500 microns and 1 mm.These aggregated small crystal clusters are difficult to apply tosubsequent scientific research and Industrial applications, such asmeasurement of transmission properties and electronic structures,large-scale spalling, and device manufacturing. Correspondingly, themethod for making the transition metal dichalcogenide crystal of thepresent application can obtain MoSe₂ crystal with a size of 3 micronsand MoTe₂ crystal with a size of 3 microns, and the MoSe₂ crystal andthe MoTe₂ crystal have regular morphologies and flat surfaces, which canbe applied to subsequent scientific research and industrialapplications. It can also be seen from FIGS. 5A-5C and FIGS. 6A-6C thatthe PtSe₂ crystal obtained by the method for making the transition metaldichalcogenide crystal of the present application exhibits a brightersurface.

FIG. 7 shows the PXRD patterns of the MoSe₂ crystals prepared by the twodifferent methods in example 1 and comparative example 1. Thecomparative example 1 has no obvious peaks, while the example 1 showssharp and strong peaks following the diffraction rule of (0 0 1), I=2n,indicating the nature of high crystallinity and the edge [0 0 1] Layersarranged in the direction. FIG. 8 shows the PXRD patterns of the MoTe₂crystals prepared by the two different methods of example 2 andcomparative example 2. Similarly, the comparative example 2 has noobvious peaks, while the example 2 shows sharp and intense peaksfollowing the diffraction rule of (0 0 1), and 1=2n.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, including inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including, the fullextent established by the broad general meaning of the terms used in theclaims.

Additionally, it is also to be understood that the above description andthe claims drawn to a method may comprise some indication in referenceto certain steps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A method of making a transition metaldichalcogenide crystal having a chemical formula represented as MX₂,wherein M represents a central transition metal element, and Xrepresents a chalcogen element, comprising: providing MX₂polycrystalline powder, MX₂ seed crystals, and a transport medium;providing a first reaction chamber defining an opening at one end of thefirst reaction chamber, wherein the MX₂ polycrystalline powder and thetransport medium are placed in the first reaction chamber; and providinga second reaction chamber comprising a source end and a deposition endopposite to the source end, wherein the first reaction chamber and theMX₂ seed crystals are placed in the second reaction chamber, the firstreaction chamber is placed at the source end, and the MX₂ seed crystalsare placed at the deposition end; and T_(H) represents a temperature atthe opening of the first reaction chamber, T_(S) represents atemperature of the MX₂ polycrystalline powder, and T_(D) represents atemperature at the deposition end of the second reaction chamber; and−15 K<(T_(S)−T_(H))<−5 K, 45 K<(T_(H)−T_(D))<55 K.
 2. The method ofclaim 1, wherein the MX₂ polycrystalline powder is obtained by directsolid-state reactions of a mixture of the central transition metalelement M and the chalcogen element X.
 3. The method of claim 1, whereinthe MX₂ seed crystals comprise a plurality of single crystals.
 4. Themethod of claim 3, wherein average sizes of the :MX₂ seed crystals arein a range from 500 μm to 1 mm.
 5. The method of claim 1, wherein amethod for providing the MX₂ seed crystals comprises: placing the MX₂polycrystalline powder and the transport medium in a chamber configuredfor chemical vapor transport (CVT) growing, to obtain MX₂ crystals;removing remaining transport medium in the MX₂ crystals; and selectingthe MX₂ crystals with sizes in a range of 500 microns to 1 mm for makingthe transition metal dichalcogenide crystal.
 6. The method of claim 5,further comprising cutting the selected MX₂ crystals to form a hexagon,a triangle, or a square.
 7. The method of claim 1, wherein the openingof the first reaction chamber is away from the MX₂ seed crystals.
 8. Themethod of claim 1, wherein the first reaction chamber is spaced apartfrom the MX₂ seed crystals.
 9. The method of claim 1, wherein the MX₂polycrystalline powder and the transport medium are away from theopening of the first reaction chamber.
 10. The method of claim 1,wherein a distance between the MX₂ polycrystalline powder and theopening is in a range from about 2 cm to about 6 cm.
 11. A method formaking a transition metal dichalcogenide crystal having a chemicalformula represented as MX₂, wherein M represents a central transitionmetal element, and X represents a chalcogen element; and the method formaking the transition metal dichalcogenide crystal, comprising: placinga MX₂ polycrystalline powder and a transport medium in a first reactionchamber; and placing the first reaction chamber and a MX₂ seed crystalin a second reaction chamber having a source end and a deposition endopposite to the source end, wherein the first reaction chamber is placedat the source end, and the MX₂ seed crystal is placed at the depositionend, and the first reaction chamber and the MX₂ seed crystal are spacedapart from each other; and T_(H) represents a temperature at an openingof the first reaction chamber. T_(S) represents a temperature of the MX₂polycrystalline powder, and T_(D) represents a temperature at thedeposition end of the second reaction chamber; and −15K<(T_(S)−T_(H))<−5 K, 45 K<(T_(H)−T_(D))<55 K.
 12. The method of claim11, wherein the MX₂ polycrystalline powder is obtained by directsolid-state reaction of a mixture of M element and X element.
 13. Themethod of claim 11, wherein the MX₂ seed crystal is a single crystal.14. The method of claim 13, wherein a size of the MX₂ seed crystal is ina range from 500 μm to 1 mm.
 15. The method of claim 11, wherein amethod for making the MX₂ seed crystal comprises: placing the MX₂polycrystalline powder and the transport medium in a chamber for CVTgrowing, to obtain a MX₂ crystal; removing remaining transport medium inthe MX₂ crystal; and selecting the MX₂ crystal with a size range of 500microns to 1 mm as the MX₂ seed crystal.
 16. The method of claim 15,further comprising a step of cutting the MX₂ crystal to form a hexagon,a triangle, or a square, after selecting the MX₂ crystal with the sizerange of 500 microns to 1 mm as the MX₂ seed crystal.
 17. A method ofmaking a transition metal dichalcogenide crystal having a chemicalformula represented as MX₂, wherein M represents a central transitionmetal element, and X represents a chalcogen element, comprising:providing MX₂ polycrystalline powder, MX₂ seed crystals, and a transportmedium; providing a first reaction chamber defining an opening at oneend of the first reaction chamber, wherein the MX₂ polycrystallinepowder and the transport medium are placed in the first reactionchamber, and the opening of the first reaction chamber is away from theMX₂ seed crystals; and providing a second reaction chamber comprising asource end and a deposition end opposite to the source end, wherein thefirst reaction chamber and the MX₂ seed crystals are placed in thesecond reaction chamber, the first reaction chamber is placed at thesource end, and the MX₂ seed crystals are placed at the deposition end.18. The method of claim 17, wherein T_(H) represents a temperature atthe opening of the first reaction chamber, T_(S) represents atemperature of the polycrystalline powder, and T_(D) represents atemperature at the deposition end of the second reaction chamber; and−15 K<(T_(S)−T_(H))<−5 K, 45 K<(T_(H)−T_(D))<55 K.
 19. The method ofclaim 17, wherein the MX₂ polycrystalline powder and the transportmedium are away from the opening of the first reaction chamber.
 20. Themethod of claim 17, wherein a distance between the MX₂ polycrystallinepowder and the opening is in a range from about 2 cm to about 6 cm.